Adverse event rate otherwise 'acceptable' in 18-month registry data

Action Points

Note that this observational cohort study of patients with NSTEMI who received the Absorb bioresorbable stent at a single center found a nearly 7% rate of death, MI, and revascularization at 18 months.

Be aware that the benefits of a bioresorbable stent are not likely to be seen until several years post-procedurally.

Scaffold thrombosis remained problematic for Absorb bioresorbable vascular scaffold implantation in real-life practice mid- to long-term, a study found, although some cardiologists suggested that truly long-term data will be needed to settle the issue.

Yet scaffold thrombosis occurred in 2.7% of patients by a year and a half, with no early cases observed.

Underexpansion was noted in 26% of the lesions studied. "Our analysis shows that underexpansion of bioresorbable vascular scaffold occurs frequently and had a nonsignificant association with an increased risk of major adverse cardiac events and probable/definite stent thrombosis," according to the authors.

"Though the rates [of scaffold thrombosis] are similar to those observed in other bioresorbable vascular scaffold trials, it is still higher compared to second generation metallic drug-eluting stents [DES]," suggested Huay Cheem Tan, MBBS, and Rajiv Ananthakrishna, MD, DM, both of Singapore's National University Heart Centre.

"Scaffold under-expansion is a known important risk factor for scaffold thrombosis and restenosis. This can be addressed if intravascular imaging modality is more commonly adopted," the pair noted in an accompanying editorial.

"With a universal adoption of optimal implantation techniques and enhanced scaffold design, it remains to be seen whether scaffold thrombosis rates will be further reduced."

"Although it is not clear why this complication is observed in high incidence with bioresorbable vascular scaffolds, a potential explanation could be the increased thickness of the bioresorbable vascular scaffold struts, which can cause convective flow patterns, potentially triggering platelet deposition and subsequent thrombosis, especially in settings with suboptimal flow conditions," van Geuns and colleagues wrote.

The BVS Expand Registry served as the source of data for van Geuns and his team. Their prospective, single-center study included 249 patients presenting with non-ST-segment elevation MI, stable or unstable angina, or silent ischemia due to a blocked coronary artery. Notably, cases of ST-segment elevation MI were excluded.

In this study population, 38.1% had type B2 or C lesions; 21.3% had bifurcation lesions; 45.6% had multivessel disease; and 42.2% presented with moderately- or severely-calcified lesions. Men accounted for 73.5% of the group, which had a mean age of 61.3.

Selection bias and the lack of direct comparison with metallic DES were two important caveats to the registry investigation, in addition to its nonrandomized design, the authors acknowledged.

Tan and Ananthakrishna, however, argued that this type of study still had its merits. Compared with what is gleaned from randomized trials, "knowledge from the registry studies do contribute to a better understanding of device-oriented patient outcomes," according to the editorialists.

The bigger issue seemed to be the availability of data on longer follow-up.

"The unique properties of bioresorbable vascular scaffolds are not expected to be obvious until 3 to 5 years after its implantation. The reported follow-up period of 18 months in this registry might be insufficient to address the potential plausible advantages of bioresorbable vascular scaffolds," they wrote.

"It is still unclear whether it should be used routinely in clinical practice, in anticipation of its potential promising long-term advantages. Perhaps, there is a need to wait a bit longer for the final verdict to be known," Tan and Ananthakrishna concluded.

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